金属转运基因在社区获得性甲氧西林耐药金黄色葡萄球菌致病中的作用

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), strains of MRSA that are able to infect healthy people in community, show more virulent than HA-MRSA and have recently arisen in many locations around the globe. The reason for enhanced CA-MRSA virulence is unclear, and the contributions of PVL and core genome -encoded virulence genes are still controversial. It has been previously shown that metal transporter genes contribute to the pathogenicity of Pseudomonas aeruginosa and Salmonella. We found series of genes encoding proteins involved in metal transport, such as isdB, fhuB, sirA and cntD, were highly up-regulated by CA-MRSA strains and higher expressed compared to HA-MRSA during culture in human serum, indicating that these genes may be related to the pathogenicity of CA-MRSA. In this project, the Asian epidemic CA-MRSA clone strains will be studied and compared with HA-MRSA strain by performing gene knockout, in vitro virulence assays and bacteremia, skin infection models in mice, to determine the role of these metal transport genes in the virulence of CA-MRSA and uncover new mechanism of high virulence of CA-MRSA. The result of this study will provide research basis that can be used to develop novel vaccines and drugs for preventing and treating of CA-MRSA infection.

CA-MRSA已呈世界性流行，其具有比HA-MRSA更强的毒力，常引起无基础疾病的社区健康人群感染。CA-MRSA高毒力的确切机制仍不明确，现有研究未能确切证实杀白细胞素(PVL)和核心基因组编码毒力基因在CA-MRSA高毒力中的作用。但已有研究发现金属转运蛋白在铜绿假单胞菌、沙门菌的毒力中发挥重要作用。本课题组前期研究发现CA-MRSA菌株在人血清中高表达isdB、fhuB、sirA、cntD等金属转运基因，其表达明显高于HA-MRSA菌株，提示这些基因可能与CA-MRSA的高毒力密切相关。本课题组拟以亚洲流行CA-MRSA克隆菌株为研究对象，并以HA-MRSA菌株作为对照，通过基因敲除、生长试验、体外毒力试验、小鼠菌血症、皮肤感染模型等，验证金属转运基因在CA-MRSA所致感染中作用，阐明CA-MRSA高毒力机制。研究结果将为有针对性地进行CA-MRSA的药物及疫苗开发提供新基础。

CA-MRSA已呈世界性流行，其具有比HA-MRSA更强的毒力，常引起无基础疾病的社区健康人群感染。CA-MRSA高毒力的确切机制仍不明确，现有研究未能确切证实杀白细胞素(PVL)和核心基因组编码毒力基因在CA-MRSA高毒力中的作用。但已有研究发现金属转运蛋白在铜绿假单胞菌、沙门菌的毒力中发挥重要作用。本课题组前期研究发现CA-MRSA菌株在人血清中高表达ABC转运蛋白基因cntD，并且通过小鼠模型证实其与CA-MRSA皮肤感染密切相关。本研究以亚洲流行 CA-MRSA克隆ST59、ST72菌株（HL1、SA268），通过基因敲除、生长试验、溶血实验，证实了cntD及cnt基因簇显著影响CA-MRSA菌株的生长能力和溶血能力，但是不同ST型中cnt基因的影响存在差异。并且通过小鼠皮肤感染模型，证实了cntD基因缺失可导致CA-MRSA菌株的皮肤感染致病力降低。同时，通过转录组分析发现，cntD基因的缺失导致CA-MRSA许多重要毒力基因psm、agr系统等表达降低，提示cnt基因簇对可能通过调控其他毒力基因表达而影响CA-MRSA的毒力。研究结果提示cnt基因簇作为一个金属转运系统，对CA-MRSA的毒力产生显著的影响，其机制可能与影响其他毒力因子的表达相关，不同克隆中cnt基因的作用存在差异。Cnt基因簇编码的蛋白有可能成为 CA-MRSA的药物及疫苗开发新的靶点。